1. Field of the Invention
The present invention relates to a feedback control system which provides failsafe operation of a controlled apparatus in the event of failure of one or more feedback transducers electrically connected to the controlled apparatus through a failsafe feedback control system.
2. Description of the Prior Art
The need for failsafe operation of an apparatus the control of which is responsive to feedback transducers is well known. Of particular concern are those instances when one or more feedback transducers fail. For example, patients are typically heated using a closed loop infrared heating system wherein heat lamps are positioned above the chest and face. One or more temperature transducers in the form of thermistors, resistance thermometers or thermocouples is installed on the skin of the patient in the area being heated. Such transducers are intended to measure skin temperature and to send signals representative of such measurement to the apparatus which controls the heat lamps to assure that the patient is not burned and temperature is controlled t desired levels during treatment. Such transducers are prone to failure in that they can be dislodged from the skin. In such instances, the dislodged transducer will no longer report the actual skin temperature being controlled. In addition to being dislodged from the skin, such transducers can fail in an open or short circuit mode with similar results. Regardless of the reason for transistor failure, the result will be that the controlled lamp apparatus will function in an unsafe manner since the skin temperature will not be maintained at the desired level.
It is an object of the present invention to provide a failsafe feedback control system wherein failure of one or more measuring transducers is compensated for in the operation of a controlled apparatus.
It is another object of the present invention to provide a failsafe feedback control system wherein dislodgement of a transducer from an object having a characteristic being measured is compensated for in the operation of a controlled apparatus performing a function upon such object.
It is a further object of the present invention to provide a failsafe feedback control system wherein if one or more transducers fail in an open or short circuit mode, the operation of the controlled apparatus performing a function upon the object being measured by such transducers will be automatically adjusted to compensate for such transducer failure.
It is a further object of the present invention to provide a failsafe feedback control system which includes two or more transducers the failure of one or more of which is compensated for.